94 BATHYMETRICAL SURVEY OF 



Loch Giorra (see Plate XXVII.). Loch Giorra (or Girre) trends 

 almost east and west ; there is a slight bend near the middle of the loch, 

 the eastern half trending north-west and south-east. It is over four- 

 fifths of a mile in length, with a maximum breadth of over a quarter 

 of a mile, the mean treadth being about one-sixth of a mile, or 20 per 

 cent, of the length. Its waters cover an area of about 88J acres, or 

 less than one-seventh of a square mile, and^ it drains directly an area of 

 over 5J square miles, but, since it receives the outflow from Loch 

 Daimh, its total drainage area is over lOf square miles an area 78 

 times greater than the area of the loch. Fifty-five soundings were taken 

 in Loch Giorra, the maximum depth observed being 49 feet. The 

 volume of water is estimated at 83,686,000 cubic feet, and the mean 

 depth at nearly 22 feet, or 44 per cent, of the maximum depth. The 

 length of the loch is 88 times the maximum depth, and 200 times the 

 mean depth. 



The floor of Loch Giorra is rather irregular. The deepest part is in 

 the western half, the maximum depth of 49 feet having been observed 

 about one-sixth of a mile from the west end. The 2 5 -feet basin in this 

 part of the loch is about two-fifths of a mile in length, and towards the 

 east end there is a second 25-feet basin about one-fifth of a mile in 

 length, in which the maximum depth is 40 feet. These two basins are 

 separated by a remarkable rise of the bottom, on which depths of 15 

 and 18 feet were recorded, surrounded 011 all sides by deeper water. The 

 area of the lake-floor covered by less than 20 feet of water is nearly 

 43 acres, or over 48 per cent, of the total area of the loch ; that covered 

 by water between 20 and 40 feet in depth is nearly 38 acres, or about 

 42 per cent. ; while that covered by more than 40 feet of water is 

 over 8 acres, or over 9 per cent. Loch Giorra was surveyed on the same 

 day as Loch Daimh (May 26, 1903) ; its elevation above the sea could 

 not be determined. 



Temperature Observations. A series of temperatures taken in the 

 deepest part of the loch gave the following results : 



Surface ... 50'OFahr. 



10 feet 48-0 ,, 



25 ,, 46-8 



45 ,, 40 -o ,, 



A comparison of these temperatures with those taken in Loch Daimh 

 later in the day shows that, while the surface temperature in each loch 

 was nearly identical, the temperature of the water beneath the surface 

 was lower in the deeper loch : thus at 10 feet the temperature in Loch 

 Daimh was 1-0 lower than in Loch Giorra, at 25 feet it was 2-8 lower, 

 and at 50 feet it was 2'5 lower than at 45 feet in Loch Giorra. 



Loch Bhac (see Plate XXVIII,). Loch Bhac (Bhaic, or Vach) lies 

 to the north of Loch Tummel, and flows by the Allt Bhaic into the river 



